In industries such as the mining industry where it is necessary to employ crushers to crush rocks, it is common place for pieces of magnetic material forming part of the crushing equipment to break off and be mixed with the crushed rock. This magnetic material, if it is left mixed with the crushed rock feed, can cause substantial harm in any downstream processing of the crushed rock feed.
In many instances, magnetic separators are therefore employed immediately downstream of crushers to remove any magnetic material whether it has been broken off from the crushers during the crushing operation or incorporated from any other source.
In the gold mining industry in particular, rock is crushed whilst being mixed with water to form a slurry. This slurry may then be introduced into a magnetic separator and allowed to pool in contact with an attraction surface such as a drum. A magnet sitting behind the opposite surface of the drum attracts magnetic particles from the slurry. As the drum rotates beyond the magnet, these magnetic particles fall off into a collection area.
Whilst magnetic separation of slurries in this fashion has proven to be reasonably effective, particularly where the particles comprising the slurry are relatively fine, there are a number of problems associated with this technique.
For instance, where are a substantial number of coarse particles in the slurry, eg. particles in a range 5 mm to 50 mm, it has been found that this technique is not effective because the step of pooling the slurry causes the coarse particles and slurry to clump and hence interfere with flow of slurry past the rotating drum.
Even in situations where the particles are relatively fine, there may be difficulties associated with clumping of magnetic material on the attraction surface when it passes the edge of the magnet with the result that the magnetic material does not separate cleanly from the drum as it rotates.
A further concern relates to the fact that particles of magnetic material attached to the drum by virtue of their strong attachment can entrain a proportion of non-magnetic material from the slurry. As a result, this non-magnetic material may be harvested together with the magnetic material rather than in a separate stream free of magnetic material. Thus, valuable components of the slurry, eg. gold may be lost.
It is an object of the invention to provide a method and apparatus which addresses one or more of the aforesaid disadvantages.